This invention relates to a method for improving starch retention in papermaking using admixtures of acrylic acid/acrylamide-type polymers. Filler retention and wire drainage are also improved, without adversely affecting sheet formation. These synergistic polymer compositions are preferably high charge density blends of high and low molecular weight anionic emulsion polymers.
U.S. Pat. No. 4,643,801 discloses the use of compositions containing a cationic starch, an acrylic acid/acrylamide copolymer and dispersed silica as binders in papermaking. The patent does not disclose, however, the instant high and low molecular weight polymer blends.
The inventors have discovered that polymer blends comprising acrylic acid/acrylamide-type polymers of different molecular weights greatly improve starch retention in papermaking. Unretained starch in a paper system may cause excessive foaming and deposit-related problems. Past practice required that mills either limit starch usage or use defoamers. Attempts to use conventional retention aids sometimes caused over-floccing, which adversely affected sheet properties. These problems are remedied by the instant method.